Conventional hairspray formulations are ethanol based and therefore form highly wetting systems for hair. Coalescence of the aerosol droplets on the hair fibre and subsequent ethanol evaporation to leave solid polymer residue leads to a network of fibre-fibre bonds. The bonding arrangement holds the hairstyle in place. As is typical of a highly wetting system, the droplet morphology of the sprayed formulation on the hair is roughly symmetrical around the fibre with a contact angle of zero or near zero degrees.
There are, however, undesirable consequences in coating hair with polymer, manifesting in perceptions of sensory negatives such as stiffness, rigid feel, stickiness or unnatural feel.
U.S. Pat. No. 4,871,529 describes ethanol solvent-based hairspray compositions which employ a specific type of silicone copolyol which causes the hairspray composition to contract upon drying. This is described as an "autophobic effect" which causes large droplets of the composition to form, and produce larger juncture points between fibres. Localisation of deposits in this way is said to give stronger bonds and greater hold.
In U.S. Pat. No. 4,871,529 the autophobic effect is achieved by a specific type of silicone copolyol, SILWET.RTM. L-7602 (ex Union Carbide), a polyethylene oxide modified dimethylpolysiloxane in which the polyalkylene oxide groups are attached along the siloxane backbone through Si--C bonds. SILWET.RTM. L-7602 is representative of a class of "alkyl-pendant" type copolyol of the following general formula: ##STR1##
In SILWET.RTM. L-7602 specifically, n=0, m.gtoreq.1 and Z is a methyl radical.
An "alkyl-pendant" silicone copolyol, for the purposes of the description, is a silicone copolyol in which polyalkyleneoxide groups are found scattered at various points, often randomly, along the length of the silicone backbone, from which they are pendant, resulting in "comb-like" structures.